Runout is the measure by which a rotating shaft deviates from being truly round. Runout is generally characterized by the difference between a highest and lowest point on the shaft as it rotates through one revolution.
Runout of a rotating tool is traditionally measured by placing a dial indicator in contact with the surface of a shaft of the tool. The shaft is then slowly turned as the range of values indicated on the dial is observed. Subtracting a lowest value from a highest value determines the runout.
Traditional means often requires the tool to be held in a pin vise or a chuck held on a machinist's bench rather than in the chuck of a motor drive for rotating the tool. Moving the tool from a bench to the tool is time consuming and slows production of product requiring the rotating tool. A better means would allow measurement of runout in place in the chuck of the motor drive.
Measuring as the tool is rotated by the motor drive at the higher speeds generally used for production is desirable. Observing runout at various speeds may indicate vibrations within the tool generated by imbalances that would not be evident in traditional (static) testing. Thus, a tool that might otherwise appear to be within tolerance by static testing might prove to be unsatisfactory in operation. Testing at operating speeds eliminates the likely spoilage of product due to imperfections not detected otherwise.
Attempting to test a rotating shaft with a dial indicator will because of the friction at the point where the indicator bears on the shaft and the high speed of the rotating surface at which it bears, tend to fling the dial indicator away from the shaft causing a hazard. Additionally, accurate measurement is not possible because of a phenomenon known as float. As the bearing surface of the dial indicator passes over a lower spot in the shaft, the indicator might not react quickly enough to remain in contact with the surface. The result is to miss a measurement on the low spot thus giving the resulting measurement an indication of lesser runout than is present.
Measurement of a fluted cutting tool is very difficult by, this means as well. The cutting edges of the tool tend to catch the tip of the dial indicator as it turns. Further, the flutes defined by the surface tend to allow the tip into the flute causing inaccuracy. Often the cutting edges will destroy the tip of the dial indicator.
Manufacturers such as Keyence® produce laser measuring-heads that accurately measure small displacements of reflective surfaces. The laser measuring-heads exploit a process known as triangulation. By shining a coherent laser beam incident to a reflective surface and then measuring the geometry of the reflected beam with respect to the incident beam, the location of the surface is determined. Such laser measuring-heads are used to measure displacement without actually making contact with the surface measured. For instance, where the metal foil output of a rolling mill must be measured for consistency of thickness, a laser measuring-head may be used to measure the height of the surface as the foil leaves the mill.
Thus, there is an unmet need in the art for using a laser measuring-head to accurately measure of runout of a rotating tool.